Abstract

We demonstrate mid-infrared (mid-IR) supercontinuum generation (SCG) with instantaneous bandwidth from 2.2 to 5 μm at 40 dB below the peak, covering the wavelength range desirable for molecular spectroscopy and numerous other applications. The SCG occurs in a tapered As2S3 fiber prepared by in-situ tapering and is pumped by femtosecond pulses from the subharmonic of a mode-locked Er-doped fiber laser. Interference with a narrow linewidth c.w. laser verifies that the coherence properties of the near-IR frequency comb have been preserved through these cascaded nonlinear processes. With this approach stable broad mid-IR frequency combs can be derived from commercially available near-IR frequency combs without an extra stabilization mechanism.

Figures (6)

(a) GVD parameter of the initial fiber, a step index As2S3 fiber with core and cladding diameter of 7 μm and 160 μm, respectively, and an NA of 0.2, compared with that of the fundamental mode of a tapered fiber with diameter of 2.3 μm, (b) GVD parameter of the fundamental mode of the tapered fiber at 3.1 μm as a function of the fiber diameter.

The output power at 3.9 μm during the tapering process (blue curve) versus the pulling length (bottom axis) and corresponding diameter of the fiber waist (top axis), and the calculated GVD parameter of the fundamental mode in the taper waist (red curve).

(a) Spectrum of the OPO output broadened by the tapered As2S3 fiber compared with the simulation result (the OPO spectrum is intentionally shifted), (b) calculated degree of coherence,
g12(1) as defined in [19].